In a bombshell adjustment to the official timeline, police said Las Vegas shooter Stephen Paddock fired on security guard Jesus Campos before taking aim at the concert crowd.

Related: Las Vegas shooting coverage

The Los Angeles Times reported Clark County Sheriff Joe Lombardo said in a news conference Monday that Paddock shot Campos  before gunning down Route 91 Harvest country music festival attendees.

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Previously, officials credited Campos with stopping the assault.

Related: Las Vegas shooting: Remembering the victims

According to officials, Campos distracted the gunman from continuing to shoot victims when he was checking on an open door alert for another room. Paddock, 64, was on the 32nd floor off the Mandalay Bay hotel when he began the shooting.

Related: Who is Stephen Paddock, the shooter killed in Las Vegas?

Officials say they don’t know why the attack stopped. Lombardo said police didn’t know Campos was shot “until they met him in the hallway after exiting the elevator.”

Police officers stand at the scene of a shooting near the Mandalay Bay resort and casino on the Las Vegas Strip, Sunday, Oct. 1, 2017, in Las Vegas. Multiple victims were being transported to hospitals after a shooting late Sunday at a music festival on the Las Vegas Strip.  (AP Photo/John Locher)

Credit: John Locher

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Credit: John Locher